 Skin
(cutaneous membrane)
 Skin derivatives




Sweat glands
Oil glands
Hair
Nails
 Protection
from mechanical damage
 Protection from chemical damage
 Protection from thermal damage
 Protection from bacterial invasion
Table 4.1 (1 of 2)
Table 4.1 (2 of 2)
 Epidermis—outer




layer
Stratified squamous epithelium
Most cells are keratinocytes- produce keratin
Often keratinized (hardened by keratin- tough
and leather-like)
Avascular- no blood vessels
 Dermis


Dense connective tissue- has abundant elastic
and collagenic fibers
Major skin area where derivatives (nails and hair)
reside
Figure 4.3
 Subcutaneous
tissue (hypodermis) is deep to
dermis



Not part of the skin
Anchors skin to underlying organs
Composed mostly of adipose tissue
 Stratum




basale (stratum germinativum)
Deepest layer of epidermis
Lies next to dermis
Cells undergoing mitosis
Daughter cells are pushed upward to become the
more superficial layers
 Stratum
spinosum
 Stratum granulosum

Layer containing sacs filled with fatty material or
keratin subunits
 Stratum


Formed from dead cells of the deeper strata
Occurs only in thick, hairless skin of the palms of
hands and soles of feet
 Stratum



lucidum
corneum
Outermost (superficial) layer of epidermis
Shingle-like dead cells are filled with keratin
(protective protein prevents water loss from
skin)
Accounts for most of the epidermis
 Summary
of layers from deepest to most
superficial





Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum (thick, hairless skin only)
Stratum corneum
 Pigment
(melanin) produced by melanocytes
 Melanocytes are mostly in the stratum basale
 Color is yellow to brown to black
 Amount of melanin produced depends upon
genetics and exposure to sunlight
 Two
layers
1. Papillary layer (upper (superficial) dermal
region)

Projections called dermal papillae
 Some contain capillary loops
 Other house pain receptors and touch receptors
2. Reticular layer (deepest skin layer)



Blood vessels
Sweat and oil glands
Deep pressure receptors
 Overall

Collagen and elastic fibers located throughout
the dermis



dermis structure
Collagen fibers give skin its toughness
Elastic fibers give skin elasticity
Blood vessels play a role in body temperature
regulation
Figure 4.4
 Melanin

Yellow, brown, or black pigments
 Carotene

Orange-yellow pigment from some vegetables
 Hemoglobin


Red coloring from blood cells in dermal
capillaries
Oxygen content determines the extent of red
coloring
 Cutaneous


glands are all exocrine glands
Sebaceous glands
Sweat glands
 Hair
 Hair
 Nails
follicles
 Sebaceous

Produce oil






glands
Lubricant for skin
Prevents brittle hair
Kills bacteria
Most have ducts that empty into hair follicles;
others open directly onto skin surface
Glands are activated at puberty
Acne is an infection of sebaceous glands
Figure 4.6a

Sweat glands



Produce sweat
Widely distributed in skin
Two types


Eccrine
 More numerous,
 Secretions containing water, salts, and vitamin C
 Open via duct to pore on skin surface
 Activated by a rise in temperature Activity controlled by nervous system
Apocrine
 Found in axiallary and genital areas
 Ducts empty into hair follicles
 Secretions contain fatty acids and protein in addition
to water and salts
Figure 4.6b
 Composition




Mostly water
Salts and vitamin C
Some metabolic waste
Fatty acids and proteins (apocrine only)
 Function



Helps dissipate excess heat
Excretes waste products
Acidic nature inhibits bacteria growth
 Odor
is from associated bacteria
 Hair



Produced by hair follicle
Consists of hard keratinized epithelial cells
Melanocytes provide pigment for hair color
Figure 4.7c
 Hair



anatomy
Central medulla
Cortex surrounds
medulla
Cuticle on outside of
cortex

Most heavily
keratinized
Figure 4.7b
 Associated

Hair follicle





Dermal and epidermal sheath surround hair root
Arrector pili muscle


hair structures
Smooth muscle
Pulls hairs upright when cold or frightened
(environmental stimuli)
Sebaceous gland
Sweat gland
Hair follicles and sebaceous glands are found
everywhere in body except soles of feet and
palms of hands
Figure 4.7a
Figure 4.8
 Nails

Scale-like modifications of the epidermis


Stratum basale extends beneath the nail bed


Heavily keratinized
Responsible for growth
Lack of pigment makes them colorless
 Nail




structures
Free edge
Body is the visible attached portion
Root of nail embedded in skin
Cuticle is the proximal nail fold that projects
onto the nail body
Figure 4.9
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